Development of advanced dielectric materials with both high‐electric energy density and high‐temperature resistant attributes is highly desirable in modern electronics and electrical systems. Herein, a series of polyimide (PI)‐based sandwich‐structured dielectric nanocomposite films have been attempted to develop the advanced high‐temperature resistant capacitor films, wherein the boron nitride nanosheets/PI nanocomposite acts as the outer layers and the zinc oxide (ZnO)/PI as the middle layer. Benefitting from the merits of both fillers and the unique structure, the resulting nanocomposite films can simultaneously achieve both high‐dielectric constant and high‐breakdown strength, as well as low‐electrical conduction loss, thus leading to improved discharged energy densities (Ue) and charge/discharge efficiency (η) at elevated temperatures. It is found that the sandwich‐structured nanocomposite film with 0.4 vol% ZnO (0.4ZnO/PI‐S) can deliver a maximum Ue of 5.29 J cm−3 at 400 MV m−1 and 150°C, which is about 1.9 times that of the pristine PI film. Moreover, outstanding dielectric stability over 10,000 charge/discharge cycles has been demonstrated in such PI‐based sandwich‐structured nanocomposite films at 150°C and 200 MV m−1. This research may provide a new paradigm to explore polymer nanocomposites having excellent energy storage and efficiency at elevated temperatures.